In the shotgun sequencing method, “random DNA fragments” are sequenced. Then, by the use of specialized software and computerized machinery, these individual fragments are assembled into one single genome sequence. This task of joining the random samples is accomplished by finding out sticky ends in random individual DNA fragments. Sticky ends of one random DNA fragment is made to join with another sticky end by finding out the complementary sequence of this sticky end on another random DNA fragment (from the whole lot). These sticky fragments are also known as overlapping fragments. Please note that this part of the task is done by using computer software. Likewise, all overlapping ends are made to join with their complementary ends; resulting in assembly of the complete genome. Therefore, shotgun sequencing is heavily dependent on computer software; but it increases the speed of the overall process of sequencing.
On the other hand, in IHGP (International Human Genome Project), “ordered genomes fragments” had been taken; so, there was no requirement to join individual fragments. So, the requirement of computer software was less. Without software also, the sequence of fragments was known.